The invention relates to a method for completing a well bore in an underground formation, said well bore being closed off by a closing structure for blocking flow of pressurized fluid through said well bore, comprising the step of passing a substantially tubular element having a tube wall surrounding an axial bore through said closing structure.
Such a method is known from practice and is carried out in the course of the completion of a well, i.e. the finalizing operations for making a well bore ready for functions such as producing oil, gas or another fluid from the formation, reservoir observation or fluid injection.
However, in badly consolidated or fractured formations these functions can be hampered by inflow of particles into the well bore. Such particles can originate either from the formation itself or from proppant materials used to support the completion, i.e. the section of the well bore that is to perform the above-mentioned function. Such a particle inflow does not only further destabilise the formation, but can also block the well bore or may entail the need of separating the particles from fluid produced by the well bore.
To overcome this problem, it has been proposed to support the production section using a supporting device to support the formation and any proppant used for completing the well.
From U.S. Pat. No. 5,366,012, it is known to install a slotted tube as supporting device. The slotted tube is radially expanded to support the formation and/or proppant material. This is carried out when the slotted tube is located at an uncased bottom section of the borehole, and involves axially forcing a mandrel through the slotted tube to make it expand radially.
In practice, as part of the completion operation, after the well bore has been provided with a casing and a closing structure, such as a blow-out preventer, a production string carrying the slotted tube is passed through the closing structure.
However, since supporting devices such as slotted tubes are provided with penetrations, to be able to safely pass the supporting device through the closing structure, it is necessary to xe2x80x9ckillxe2x80x9d the well, by balancing the upward pressure of e.g. oil or gas in the formation with a fluid column in the well bore to avoid fluid flow from the well via the penetrations in the wall of the supporting device.
However, balancing a well is a time consuming operation which may also damage the formation and/or leave the well in an unsafe, uncontrollable condition.
It is an object of the invention to provide a solution which allows the completion of an uncased section of a borehole, without having to balance the well.
According to one aspect of the present invention, this object is achieved by carrying out a method of completing a borehole in accordance with claim 1.
This way, pressurised fluid in the well is substantially prevented from passing the penetrated closing structure, because the tube wall which is to complete the uncased section is impermeable to any pressurized fluid in the well as it penetrates and passes through the closing structure. Portions of the tube wall having been brought in position or having at least passed the closing structure are made permeable, so that fluid can be received via the initially impermeable tube wall.
According to a further aspect of the invention, a pressurized drilling fluid is axially fed through said tubular element before said processing is carried out. This way, the drilling fluid can be used to power the drill and does not prematurely radially exit the tubular element through the circumferential openings.
According to another aspect of the present invention, the above-mentioned object is achieved by providing a tubular element in accordance with claim 10.
This tubular element can be passed through a closing structure for blocking a flow of pressurised fluid through a well bore, while a pressure drop over the closing structure exists without allowing fluid to the closing structure via the bore of the tubular element. In its production position, the tubular element can be made permeable to allow the fluid to be obtained from the well to pass into the production string via the tubular element.
Particular embodiments of the method and of the tubular element according to the invention are set forth in the dependent claims.
Further objects, features, advantages and details of the invention are described with reference to embodiments shown in the drawings.